LeetCode-in-Java
264. Ugly Number II
Medium
An ugly number is a positive integer whose prime factors are limited to 2, 3, and 5.
Given an integer n, return the nth ugly number.
Example 1:
Input: n = 10
Output: 12
Explanation: [1, 2, 3, 4, 5, 6, 8, 9, 10, 12] is the sequence of the first 10 ugly numbers.
Example 2:
Input: n = 1
Output: 1
Explanation: 1 has no prime factors, therefore all of its prime factors are limited to 2, 3, and 5.
Constraints:
1 <= n <= 1690
Solution
public class Solution {
public int nthUglyNumber(int n) {
int[] ugly = new int[n];
int i2 = 0;
int i3 = 0;
int i5 = 0;
int ugly2 = 2;
int ugly3 = 3;
int ugly5 = 5;
int nextugly;
ugly[0] = 1;
for (int i = 1; i < n; i++) {
nextugly = Math.min(Math.min(ugly2, ugly3), ugly5);
ugly[i] = nextugly;
if (nextugly == ugly2) {
i2++;
ugly2 = ugly[i2] * 2;
}
if (nextugly == ugly3) {
i3++;
ugly3 = ugly[i3] * 3;
}
if (nextugly == ugly5) {
i5++;
ugly5 = ugly[i5] * 5;
}
}
return ugly[n - 1];
}
}